This invention is directed to a method of copolymerizing ethylene with cycloolefin monomers, often referred to as norbornene-type, or NB-type. More specifically, the method employs neutral nickel catalysts and the polymers obtained by the method of this invention are amorphous addition copolymers which may be random or alternating in character.
Addition copolymers of ethylene and norbornene-type monomers are well known and can be prepared using a variety of catalysts disclosed in the prior art. This general type of copolymers can be prepared using free radical catalysts disclosed in U.S. Pat. No. 3,494,897 (Reding et al.); titanium tetrachloride and diethylaluminum chloride as disclosed in East German Patents 109,224 and 222,317 (VEB Leuna); or a variety of vanadium compounds, usually in combination with organoaluminum compounds, as disclosed in European Patent Application No. 156464 (Kajiura et al.). The copolymers obtained with these catalysts are random copolymers. U.S. Pat. No. 4,948,856 issued to Minchak et al. (B.F.Goodrich) discloses preparing generally alternating copolymers by the use of vanadium catalysts which are soluble in the norbornene-type monomer and a co-catalyst which may be any alkyl aluminum halide or alkylalkoxy aluminum halide. European Patent Application No. 0 504 418 Al (Matsumoto et al.) discloses copolymerization of said monomers in the presence of catalysts such as transition metal compounds, including nickel compounds, and a compound which forms an ionic complex with the transition metal compound or a catalyst comprising said two compounds and an organoaluminum compound. More recently, metallocene catalysts were used to prepare copolymers of cycloolefins and .alpha.-olefins as disclosed in EP 283,164 (1987) issued to Mitsui Petrochemicals and EP 407,870 (1989), EP 485,893 (1990) and EP 503,422 (1991) issued to Hoechst AG. Most recently PCT published application WO96/23010 discloses processes of polymerizing ethylene, .alpha.-olefins and/or selected cyclic olefins which are catalyzed by selected transition metal compounds, including nickel complexes of diimine ligands, and sometimes also a cocatalyst. This disclosure provides, however, that when norbornene or a substituted norbornene is used, no other olefin can be present.